When you create an activity and tick "Send invitation e-mail" in the desktop version of Act! and hit ok you will see the process of creating the email and then Act! will crash. See screenshots below. Are all Outlook related bugs fixed now of is this still an outstanding one?

Re: Act! Crashing when you try to send email invifation

We address the issues with Update 2 for Build 8201. but the following week Microsoft released build 8229 which has caused new issues to appear.

While I know of issues with Act crashing when attempting to 'Write > Email (From template)' I am not familiar with this one.

We presently have a work around for the email template which appears to stop Act crashing when integrating by using either Write > Email message, clicking on an email within the Email field or using the Big email button from the top of the screen.

If you could try one of those methods and if they integrate correctly would you be able to try sending an email invitation after.

Re: Act! Crashing when you try to send email invifation

Did you try the workaround? It worked for us. Another customer had the same issues and we followed this workaround and also worked. Not ideal but Swiftpage will hopefully release a hotfix as some stage.

When you open Act! and at the record view, click on the email button and a blank email should open. Close this and you should be good to go. Also this issue only happens if you are using Outlook 2016.